Many kinds of mobile hydraulic equipment, such as agricultural sprayers, are parked outside overnight. On cold mornings, the equipment needs to warm up, and certain hydraulic functions may be sluggish until they have been operated several times and until the oil temperature has warmed up. This is particularly true of service brakes and implement hydraulic circuits, where the oil in the hydraulic lines and valves does not move or warm up until a command to operate them is given.
Additionally, it should be noted that agricultural sprayers and many other kinds of mobile hydraulic equipment use parking brakes that are released by pressurized hydraulic oil. While the equipment is parked, oil associated with releasing the parking brake is not used. Typically, the parking brake circuit contains a two-position, three-way valve that directs a small amount of flow from a constantly-pressurized hydraulic supply to the parking brakes when the operator wishes to release the brakes. The constantly-pressurized hydraulic supply is oftentimes delivered by a gear pump running over a low pressure relief. This hydraulic supply for the parking brakes usually just runs over a relief valve while the equipment is parked and idling, which is not an efficient use of the oil capacity.